Arkansas Perc Test Requirements for Septic Systems

Arkansas perc test requirements start with a simple number: your soil has to drain at a rate between 15 and 75 minutes per inch to qualify for a standard septic system. The test itself must be run by a state-certified Designated Representative, not the property owner, and it has to cover both a primary drain field location and a secondary reserve area on the same lot. The Arkansas Department of Health (ADH) sets every rule that governs how the holes are dug, soaked, and timed, and the resulting rate determines how large your absorption field needs to be.¹

You Cannot Run Your Own Perc Test

Act 402 of 1977 restricts perc testing to certified Designated Representatives (DRs) who hold a current state certificate and have demonstrated competency to the local Authorized Agent. The people who qualify are:²

Registered professional engineers
Registered professional land surveyors
Registered professional sanitarians
Licensed master plumbers
Other similarly qualified individuals with education and experience in soil science, evaluated case by case

The DR you hire handles the full process, from digging soil pits through designing the system, and signs the permit application certifying the work was done according to ADH rules. Their name stays attached to the file if problems come up later.³ Permit applications and inspections are handled locally by the Environmental Health Specialist at your county health department.⁴

Soil Pits Come First

Before any perc testing happens, the DR digs soil pits to see whether the ground is even worth testing. The ADH requires a minimum of two pits: one in the proposed primary absorption area and one in the proposed secondary area. Each pit must be at least 2 feet wide, 4 feet deep unless bedrock or an impervious layer stops the digging sooner, and have an exposed sidewall at least 3 feet long.¹

The DR uses those pits to record depth to seasonal water tables, bedrock, and any impervious layer. Pits stay open so the local Environmental Health Specialist can verify what the DR found. Only after the soil passes this initial evaluation does the perc test itself proceed.

Both a Primary and a Secondary Area Are Required

Every lot must have two qualifying absorption areas: the primary drain field and a secondary area that serves as the site for a replacement system if the primary ever fails. Both must meet the same setback requirements and both must have suitable soil for a standard system. At least one perc test hole has to go in the secondary area in addition to the holes in the primary area.¹

If your lot cannot accommodate two qualifying areas, no permit for a standard system will issue, however well the primary area drains. This is worth checking before you buy a small parcel.

How the Test Is Set Up and Timed

The ADH rules call for three or more test holes spaced evenly across the primary absorption area, plus at least one in the secondary area. Standard holes are 12 inches in diameter and 18 inches deep, though depth can be adjusted to match the proposed bottom of the absorption trench if site conditions call for something shallower or deeper.¹

Before timing starts, every hole is pre-soaked. The DR fills each hole with clear water to at least 12 inches above the gravel layer and maintains that level preferably overnight, but for no less than four hours. An automatic siphon can help hold the level steady. Saturating the soil this way simulates wet-season conditions and lets clay in the soil swell fully so the reading reflects the slowest realistic drainage the ground would show through the year.¹

After saturation, the DR adjusts the water in each hole to six inches above the gravel, then measures the drop from a fixed reference point after 30 minutes. That drop converts to a percolation rate in minutes per inch. Fast-draining soils get a modified procedure: if the first six inches soaks away in less than 30 minutes after saturation, the test switches to 10-minute intervals over a full hour, and the drop during the final 10-minute interval sets the rate.¹

What Rate Passes and What It Means for Field Size

The ADH loading chart runs from 15 to 75 minutes per inch. Soil slower than 75 mpi is classified unsuitable for a standard system because sewage will back up or surface in the yard. Soil faster than 15 mpi is not assigned a standard loading rate because effluent moves through the ground so quickly that naturally occurring bacteria do not have time to treat it before it reaches the water table.¹

Between those limits, the rate drives the size of your absorption field. A faster rate closer to 15 mpi lets you use a smaller field because each square foot handles more wastewater. A slower rate closer to 75 mpi requires a proportionally larger field. The absorption area sized from perc test data can never be smaller than what seasonal water table data would require for the same site, and both the primary and secondary areas must be increased 25 percent beyond the calculated minimum.¹

Setbacks Can Disqualify Otherwise Good Soil

Passing the perc test is not enough on its own. The absorption field must also clear minimum distances from wells, water bodies, structures, and property lines. The ADH minimums are:

100 feet from any domestic water supply (private well)
100 feet from any stream, lake, or pond on adjacent property
100 feet from any sinkhole
300 feet from any spring used as a public water supply
300 feet from the high-water mark of a water body within a quarter mile of a public water supply intake
50 feet from any pond on the same property
10 feet from dwellings, buildings, property lines, and water service lines

Both the primary and secondary areas have to satisfy every one of these setbacks.⁵ Ask the DR to map the setbacks before digging test holes so you are not paying to test ground that cannot legally hold a system.

If the Soil Fails

A rate outside the 15-to-75 mpi window does not automatically kill the project. It rules out a conventional gravity-fed system with standard absorption trenches, but Arkansas allows alternative onsite wastewater systems for challenging sites. These require their own site evaluation and generally cost more to install and maintain.

Common alternatives include aerobic treatment units, which inject air into the treatment process to produce cleaner effluent and can work with smaller drain fields; drip irrigation systems, which distribute treated wastewater through buried tubing instead of relying on absorption trenches; and sand filter systems, which run effluent through engineered sand and gravel beds before dispersal. The ADH must approve any alternative design, and the permitting involves more detailed engineering than a standard perc-and-trench setup.

If none of those work for the site, the remaining paths are connecting to a municipal sewer (if one is nearby) or walking away from the lot. Running the perc test early, before committing to a property, is how most experienced buyers and builders avoid that last outcome.

Permit Validity

A construction permit issued off a passing perc test is valid for one year from the date of approval. If you do not start building within that year, the permit must be re-validated by either the original Designated Representative or the ADH’s Authorized Agent. The local Environmental Health Specialist can also void a permit before construction begins if site or soil conditions have changed since approval, or if any information on the application turns out to be inaccurate.¹ Government filing fees for the permit are set by the size of the structure being served and range from $30 for 1,500 square feet or less up to $150 for structures over 4,000 square feet; repairs and alterations are $30. The DR’s professional charges for the soil evaluation, perc test, and system design are separate.⁶

1
Arkansas Department of Health. Rules Pertaining to Onsite Wastewater Systems
2
Arkansas Department of Health. Act 402 of 1977
3
Arkansas Department of Health. Individual Onsite Wastewater System Permit Application – EHP-19
4
Arkansas Department of Health. Onsite Wastewater
5
Arkansas Department of Health. Rules Pertaining to Onsite Wastewater Systems – Section 6.2
6
Arkansas Department of Health. Onsite Wastewater Fee Schedule